The most typical method for inspection of components including leads is with 1 2-D or intensity-only sensor, i.e., a camera of some sort. These methods cannot directly provide lead coplanarity information. These methods are subject to false-calls and poor performance (accuracy, repeatability, and robustness) due to chaos in the intensity information coming from the component leads, the solder paste deposits, and the PCB.
Component placement inspection before reflow is necessary to minimize defects in the SMT process. Rework cost at this point is lower than after reflow, since components can be repositioned, added, or replaced without the need to de-solder or re-solder the components.
Utilizing 3-D inspection allows for real-time process control feedback of the placement operation. 3-D inspection can be used to assess stability and capability of the placement systems.
Inspection can also be done after reflow, but this is the most difficult point to rework and correlate. Typical rework costs are highest at this point. The reflow process time between component placement and after reflow is on the order of 10–15 minutes and does not allow for real-time corrective action and process control. Recurrent problems with placement equipment are not caught early enough to prevent production of multiple bad boards.